US 20050265546 A1 Abstract In the encryption/decryption method, a random number sequence {r
_{i}} is generated on the basis of a given multiple-affine key system K and encryption is performed by an exclusive OR of the random number sequence {r_{i}} with a plain text. Further, the multiple-affine key system K is automatically sequentially rewritten into a series of new multiple-affine key systems each time when the number of use times of the multiple-affine key system reaches a predetermined number and encryption of plain texts thereafter is continued while generating random numbers using the series of the rewritten multiple-affine key systems. Likewise, in decryption as well, since decryption is performed using a multiple-affine key system automatically rewritten each time when the number of use times reaches a predetermined number, a third party cannot reproduce the multiple-affine key system and therefore cannot decipher a cipher text. Claims(5) 1-29. (canceled) 30. A random number generating method comprising:
generating a random number sequence on the basis of a key data; counting a number of use times of the key data; and rewriting the key data, when the number of use times of the key data reaches a predetermined number, and generating a random number sequence on the basis of the rewritten new key data. 31. A random number generating method according to generating a cipher text by operating an exclusive OR of the random number sequence generated, with a plain text to be encrypted. 32. An encrypting method comprising:
generating a random number sequence on the basis of a key data; counting a number of use times of the key data; rewriting the key data, when the number of use times of the key data reaches a predetermined number, and generating a random number sequence on the basis of the rewritten new key data; and encrypting a plain text by operating an exclusive OR of the generated random number sequence with the plain text, and generating a cipher text. 33. An encrypting method according to decrypting the cipher text by operating the exclusive OR of the random number sequence with the cipher text, and generating the plain text. Description The present invention relates to an encryption method, an encryption communication method and an encryption communication system, which all employ a stream cipher that cannot be deciphered with ease. A stream encryption method has hitherto been known, which can process data easily and fast. A steam encryption method is to generate a random number sequence {r A conventional stream encryption method, however, cannot achieve a sufficient protection against a known plain text attack. There have been contrived various methods to avoid the known plain text attack. However, these methods cannot completely protect a stream cipher against the known plain text attack. Besides, security cannot be guaranteed and an encryption key can be specified with ease by the known plain text attack, though a stream cipher can be generated using pseudo-random numbers. For example, the Lehmer method, being one of random number generation methods, is to define a random number for integers (a, b and m) with
However, a random number sequence {r Thus, even with a specific algorithm for pseudo-random number generation, an encryption key can be found by specifying undetermined factors or the like if there are a sufficient volume of encrypted data. Further, a secure cipher can not be formulated with only one time multiplication by an integer. In view of the drawbacks in the stream cipher, a so-called chaos cipher has been made its debut for several years. The chaos cipher is a cryptosystem characterized by high security, and a random number sequence {x As well known, a number sequence {x A plurality of such random number sequences {y In this method, a random number sequence in real number is partly masked and only partial information is utilized for encryption so that an encryption key is difficult to be specified. According to this encryption method, an advantage is obtained since high-speed encryption has been realized by only software without use of a specifically prepared chip as under DES. However, there has still been a drawback that, even when a chaos cipher is employed, encryption can not be completed unless two or more times of multiplication by a real number is operated and therefore, a long time is required for operation of encryption processing. Also, since operation in real number is different in way of mounting according to a compiler or a model of a processor, a chaos cipher essentially has a processor-model dependency, which results in lack in versatility in application. Accordingly, there has been desired that an encryption technique that enables high-speed encryption and provides a cipher which can not be deciphered. Further, an encryption technique with versatile applications has been on demand. The present invention has been achieved in order to solve the above problem and it is an object of the present invention to provide an encryption method and an encryption system with versatile applications, which enable high-speed encryption, and whereby a cipher that cannot be deciphered can be generated. The present invention recited in claim In the first embodiment, which has the above described feature, random numbers are generated for encryption using a multiple-affine key system whose contents are automatically rewritten each time when the number of use times of the multiple-affine key system reaches a predetermined number. If a third party who tries to illegally decrypt a cipher text temporarily succeeds in deciphering a key for generation of random numbers, the key is rewritten and eventually, the third party cannot decrypt the cipher text. Therefore, high security encryption/decryption can be realized by this method. Further, the present invention specified in claim The first embodiment is to specify a particular feature of the multiple-affine key system of the present invention. In the embodiment, a multiple-affine key system constituted of a plurality of affine keys defined with 4 integers including two integers a and b, the number c of use times and a key life time n. Thereby, particular forms of a multiple-affine key system are apparent. Further, the present invention specified in claim The second embodiment is to show a case where the multiple-affine key system is simply not given in the encryption method but generated from the secrete key data and the initial random number sequence, thereby providing an encryption method with higher security is provided. Further, the present invention specified in claim The first embodiment, as described above, is to specify not only an encryption step but also a decryption step for decrypting a cipher text to a plain text by random numbers generated from a multiple-affine key system likewise. Herein, the same random numbers are generated by a multiple-affine key system in a procedure similar to an encryption step and the same rewriting is performed between encryption and decryption steps. Further, it is shown that encryption and decryption are performed by an exclusive OR. The present invention specified in claim The fourth embodiment, as described above, shows a case where encryption/decryption using a multiple-affine key system of the present invention is applied to a communication apparatus through a network and a communication system with high security can be established by an automatic rewrite function of a multiple-affine key system. Further, the present invention specified in claim The fifth embodiment provides a communication apparatus with high security in which a multiple-affine key system is not given at start of processing but is generated by given initial random number sequence data. Further, the present invention specified in claim The seventh embodiment is to apply a multiple-affine key system of the present invention to an authentication method of, for example, a credit card and there is provided an authentication method, by which authentication of an individual person or the like is enabled over communication with high security. The present invention specified in claim The ninth embodiment is a computer program operated on a computer, which is applied with a multiple-affine key system of the present invention. The application program detailed in the figure enables encryption/decryption of any digital data as an object and realizes high security. Further, the present invention specified in claim The tenth embodiment is to apply a multiple-affine key system of the present invention in a medium recording/reproduction device that performs recording to/reproduction from a record medium as an object on which digital data is stored and the multiple-affine key system of the present invention is applicable to any record medium that accepts digital data, such as a floppy disk driver and MO and high security is attained. The present invention specified in claim The eleventh embodiment is application of a multiple-affine key system of the present invention to an optical disk recording/reproduction device that performs recording to/reproduction from an optical desk as an object in which digital data is stored. This means a recording/reproduction device that records on and reproduces from, for example, CD-R and DVD on which recording/reproducing a moving picture and the like and thereby there is provided an optical disk recording/reproduction device which blocks reproduction and reading by a third party using a multiple-affine key system capable of self-rewriting, so that a copyright is surely protected. The present invention specified in claim The twelfth embodiment is to specify a case where a multiple-affine key system of the present invention is applied to a so-called portable phone and there is provided a radio transmission/reception device which perfectly prevents wire tapping by a third party by performing communication using encryption and decryption with a multiple-affine key system having an automatic rewriting function. Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention. Below, embodiments according to the present invention will be detailed with reference to the accompanying drawings. In the embodiments described below, an encryption method, an encryption communication method and an encryption communication system with versatile applications, which enable high-speed processing, and which makes deciphering impossible by providing a stream cipher in which a perfect random number sequence is used only once. The first to twelfth embodiments will be described in the following order. The first to third embodiments are ones of an encryption/decryption method. The fourth to sixth embodiments are ones of a first to third communication apparatuses employing the encryption/decryption method. The seventh embodiment is one of an authentication method employing the encryption/decryption method. The eighth embodiment is one of a network system (routers and the like) employing the encryption/decryption method. The ninth embodiment is one of an application computer program employing the encryption/decryption method. The tenth embodiment is one of a disk drive employing the encryption/decryption method. The eleventh embodiment is one of an optical disk recording/reproduction device employing the encryption/decryption method. The twelfth embodiment is one of a mobile phone employing the encryption/decryption method. The first embodiment is to specify fundamental encryption and decryption methods employing a multiple-affine key system of the present invention. In the embodiment, a principle of generation of a random number suited for stream encryption has been searched in order to eliminate a fault of a conventional stream cipher and as a result, encryption/decryption has been able to be realized, which provides a cipher that cannot actually be deciphered, and which enable high-speed processing, adopting an encryption method described below. Description will be made of outlines of encryption of the embodiment. In the embodiment, stream encryption, which cannot achieve a sufficient protection against a known plain text attack, and conventionally has not been used, is performed using a multiple-affine key system (the multiple-affine key system is a feature of the present invention, a coefficient of each of plural multiple-affine key systems is used as a secret key and the secret key (coefficient) is rewritten each time when the number of use times reaches a predetermined number, and therefore a third party who tries to decipher can be refused). It has been proved by Shanon that there is no decipherment method for a Vernam cipher, which is a stream cipher, in which a perfect random number is used only once. This means that a perfect encryption that enables high-speed processing can be established if a known plain text attack is eliminated and a generation method for a good quality random number sequence is found. The present invention has contrived a pseudo-random number generation method to which an undetermined coefficient method cannot be applied and has realized encryption with high reliability by generating a stream cipher with random numbers generated by the generation method. Particularly, in the present invention, a random number sequence with a good quality are generated using a multiple-affine key system and besides, a coefficient of the multiple-affine key system is rewritten each time of a new start after a prescribed number of generation times of a multiple-affine key system. That is, a multiple-affine key system rewritten each time of a new start after a prescribed number of the generation run times is used as a key in encryption/decryption which is hard to be deciphered by a third party and besides, a plurality of multiple-affine key systems are prepared and the plurality of keys are cross-referenced to automatically update their coefficients in rewriting, whereby deciphering by a third party who employs an undetermined coefficient method is excluded. Namely, the present invention provides a method in which a lifetime of a key is defined and an aged key (a coefficient of a multiple-affine key system) is automatically rewritten by a new key, i.e, a method in which a good quality random number sequence {r [Description of Affine Key] Description will be made of a multiple-affine key system that is used in the embodiment below. An affine key according to the present invention corresponds to a coefficient of a multiple-affine key system for generation of a random number sequence that is used in encryption. An affine key is automatically updated each time of a new start after the prescribed number of generation times of a random number sequence using the multiple-affine key system, thereby perfectly excluding deciphering by a third party. Assuming a finite field F, the finite field F can be realized by designating a aggregation of integers and an operation on the aggregation. For example, the finite field F can be expressed as F=Z/(p) (p is a prime number) or a galois field of a characteristic p. An affine key on the finite field F can be expressed by four integers K={a, b, c, n} and an action of an affine key K on an integer x ε F is defined as follows:
Practically, a multiple-affine key system is adopted in which a plurality of affine keys are employed instead of a single affine key. A multiple-affine key system comprises: when the number of keys is set to M, a plurality of affine keys {K[i]} (0≦i≦M-1) and one procedure showing key rewriting processing : procedure w (i, j: integer) in the sense of a structure expression: procedure w (i, j: integer);
In this procedure, a coefficient a of the ith affine key K[i] to be rewritten can be found to be rewritten based on coefficients a and b of the jth affine keys K[j] as a reference in the rewriting. Further, a coefficient b of the ith affine key K[i] to be rewritten can be found to be rewritten based on coefficients a and b of the jth affine key K[j]. Encryption can be realized by software and each K[i] is initialized one way or another when the software is started. Unless specifically stated, K[i].b=3 for the reason describe later. Even when control is effected in start of encryption such that an affine key is initialized, a cipher text cannot actually be deciphered as described later. [Generation Method for Cipher Text] A procedure of encryption/description of a plain text by a multiple-affine key system which is the first embodiment of the present invention will be described using flowcharts of In Step i An initial value x That is, at first, an initial value x Step ii Then a plain text mi is read in (S Then, if K[kn].c is equal to or less than the set number n of times, since there is no necessity of key updating, an exclusive OR is performed on the generated random number sequence {r Step iii Further, here n is expressed as the upper 8 bits of x and thereby, an affine key K used at the next stage is specified (S Step iv If K[i].c≧K[i].n, w (i, j) is executed, the result is K[i].c=0. Namely, if the number of times has reached the number of times at which rewriting is required, the procedure w (i. j) for the rewriting is executed and the coefficients a an b of the multiple-affine key system are rewritten (S Step v i=j is set. Program flow returns to the step ii and processings from step ii to step v are repeated on following communication texts. In the flowchart of In this case, since a multiple-affine key system {K[i]} is rewritten in the same way at the other communication party, both parties can share common key information as far as synchronization is retained and therefore, can perform communication and the like without including encryption key information in communication texts in both ways. [Deciphering Method for Cipher Text] Description will be made of deciphering processing of a cipher text by a multiple-affine key system of the present invention using the flowchart of That is, there is a necessity to generate a random number sequence similar to in the case a cipher text is generated and accordingly, when a setting of a multiple-affine key system K, and initialization (S Therefore, a procedure of generating a random number sequence (S Finally description will be made of a decryption part. While in the encryption, an exclusive OR is performed of the plain text mi with the random number sequence {r [Nature of Ransom Number Sequence] A random number sequence {r From the above description, multiple-affine key system encryption that generates a stream cipher using a multiple-affine key system apparently has very high security. In such a manner, a random number sequence {r For example, a good result can be obtained in numerical integration using the Monte Carlo method as well and even in an general operation that requires immensely voluminous computational time, a good result with a little error can be achieved in a little computational volume if each operation result is evaluated while repeatedly conducting prescribed times of operations using random numbers generated in the above method. Hence, by applying thus obtained random number sequences to various processings using random numbers, good results with uniformity can be attained. In the embodiment, a random number sequence {r In encryption of the embodiment, the number of keys are not definite and even if the number of keys is increased, no adverse influence is visibly exerted on an encryption speed. The number of keys is usually in the range of 2 to 2 [High Speed Processing for Cipher] In an embodiment described below, the following method is employed in order to realize high-speed encryption/decryption while taking the above described circumstances into consideration and therefore, one time multiplication is sufficiently executed for generating one random number. Further, updating of an affine key at a given probability can be realized with two-time multiplication and a division that requires a comparatively long computational time is not required. When the upper limit of updating of a key is a constant N=K[i].n, 2/N times of multiplication by an integer are on average employed to an updating of a key. That is, the average number of multiplication times by an integer per one byte is {1+(2/N)=(N+2)/N}. When N=3, a value of the average times is of the order of 1.666 . . . . That is, while the longer an encryption key, the higher the security, multiplication by an integer is less than 2 times per one byte on average. K[i].a and K[i].b are unknown numbers of 4 bytes in total as viewed from an attacker against a cipher and when N=3, if random numbers each with 3 bytes are employed in the encryption, the key is rewritten. Hence, an affine key system is extremely secure. When n Some of the affine keys have a lifetime of n The value is 1.0618 in a case where M=32, the number of keys of n Further, when the number of affine keys is increased, a degree of security is increased due to more keys than with an initial case, but an encryption speed is slightly increased. Accordingly, it is more advantageous as the number affine keys is larger as far as the increase is still accepted in a primary cache memory of CPU. When the encryption method described above is adopted, an excellent effect that an encryption processing speed does not decreased even if a degree of security is higher can be obtained. [Proof of Impossibility of Deciphering of Ciphertext] Description will be made of security of the encryption method of the embodiment described above. It is only the Vernam cipher that has been proved that no way to deciphering is available. The Vernam encryption technique requires a perfect random number sequence with a length same as a plain text as a secret key which is impractical. An cipher of the embodiment is a practical cipher that is improved from the Vernam key solving such a problem and therefore, the cipher of the embodiment has a perfect confidentiality in the following sense. That is, a multiple-affine key system K={K[i]} employed in encryption of the embodiment is considered. If lifetimes of all the affine keys K[i].n, are for example, 3, at this point, perfect confidentiality of a cipher text with 3 bytes is established. The reason why is confirmed by experiments described below. Incidentally, assuming a case of one key, if confidentiality of a cipher text can be proved in the case, the same apparently applies to a case of a multiple-affine key system. Now, it is assumed the following processing is performed with an affine key being K. Step i A random number sequence r Step ii K={a, b, c, n} is set and the upper 8 bits are indicated by a Step iii Here, one of a Step iv When a Therefore, even if deciphering is tried with the algorithm, which leads a result that solutions are obtained in number close to infinity, it is impossible for an attacker to specify a correct one of those solutions resulted from the deciphering. In other words, as for a cipher with 3 bytes, the proof has been done that there is no means for deciphering an cipher of the embodiment. Besides, when a general multiple-affine key system K={K[i]} is considered and it is further assumed that lifetimes K[i].n of all affine keys are set to 3, the proof can be done by the following method that a cipher by the multiple-affine key system has no way of deciphering. At first, it is assumed that random numbers each with 3 bytes are generated by k[ Then, it is assumed that K[ It is further assumed that K[ When the number of keys in the multiple-affine key system K={K[i]} used here is set to N, the number of possible multiple-affine key system systems is more than p Accordingly, if the lifetime K[i].n of only one key of multiple-affine key systems is 3, there is as a matter of fact no way of deciphering, which leads the fact that the cipher of the embodiment cannot be deciphered regardless of lifetimes of the other keys. [Description of Practical Model] A practical model of the above described encryption will be described. In the practical model of a most secure example, a finite field is F=Z/(p), where p=65521, the number of affine keys is 32, a timing of rewriting is K[i].n=3, where K[i].c=K[i].a(mod 3). A secret key in this case is 64 integers of the 16 bits. An initial value is desired to be attached to the head of each cipher text. For example, it may be predetermined that after processing in which random numbers are generated with an initial value as a start using a multiple-affine key system is executed the prescribed number of times, random numbers generated and a state of a key at this time are used in encryption. When this method is adopted, a known plain text attack can effectively be blocked. In this case, the total number of affine keys is
In the first embodiment described above, a method in which an initial value x The second embodiment, as shown in In the mean time, in the second embodiment as well, description will be made of a case where a finite field same as in the first embodiment described above is employed as an example. In this case, there are conceived “first method” and “second method”. [Application to Communication Between Groups] A method which will be described below is suited to a case where a communication party performs communication with a plurality of other communication parties {Bob <First Method> Step i In Step ii A random number sequence {r Step iii Thereafter, as in A rewriting processing ( The communication party (Alice) who has received the cipher text decrypts the cipher text according to the following procedure. Step i In Step ii Then, the random number value x The rewriting processing ( With the above processings, decryption of a cipher text can be realized. Since a third party who has no common secret key H cannot have any knowledge of the multiple-affine key system K, the third party cannot decipher the cipher text. Further, since this method uses a virtually different key each time, security can forever guaranteed. However, an initial vector V with 130 bytes is attached to the head of a cipher text each time of deciphering. This part of processing can be simplified as follows according to an application. That is, an initial value x A procedure of communication control in this case will be described below: <Second Method> Step i The other parties {Bob Step ii A multiple-affine key system K is generated using key transformation information (α′, β′) from the secrete key H. Further, a new multiple-affine key system K={K Step iii Then, random numbers r In a case where the cipher text is deciphered as well, likewise, random numbers r The third embodiment is to specify an embodiment in which processing speed is increased by simplifying a computational method used in random number generation. That is, here, when Z/(p): (p=65521) is used as a finite field, a computation of (mod p) is conducted along with multiplication by an integer. Since the computation of (mod p) is performed in a delayed timing by one or more times of multiplication by an integer, it will be studied whether or not the computation (mod p) can be replaced with a higher speed “and (2 When all computation is executed by a method in which the computation is replaced with “and (2 In the above described method as well, however, a computation in the case of K[i].b=0 is simply multiplication by an integer and if K[i].a is an even number, a random number to be generated has a high probability to be 0. Therefore, in the case of K[i].b=0, K[i].b=0 is forcibly rewritten into K[i].b=1. Further, in the case of K[i].a=0, since the same key is repeatedly used, K[i].a is changed to 17, where a cycle of multiplication is long. A number Below, description will be made of an encryption algorithm stepwise. [Encryption Algorithm Using and] A multiple-affine key system K={K[i]}, where K[i]={a, b, c, n}, is discussed. A random number computed in (mod p) is used as {a, b, c, n}. Further, p=65521 is set. Herein, a function of an affine key K[i] on an integer x is assumed to be as follows:
It has been already described that when this computation is applied even to rewriting of a key, complexity of a key cannot be maintained. Further, since disorders sometimes occur in random numbers to be generated, though at a low probability, a procedure w (α, β) for rewriting is altered in the following way in the third embodiment:
With the above change, encryption is accelerated and complexity of a multiple-affine key system can be maintained. Incidentally, a number 17 is one of primitive roots and another primitive root exerts a similar effect. A unit of (computer) processing is set to 16 bits, this is because a processing unit of a control section is 16 bits (byte unit) and because the 16 bits are divided into the upper 8 bits and the lower 8 bits in the processing. The largest prime number in the 16 bits is P=65521 and thereby the value is utilized. In a case where a processing unit is not a byte unit in the control section, the processing unit is not limited to the above one. [Procedure for High-Speed Encryption] There is below shown a procedure for encryption in the third embodiment which enables the highest speed encryption. A communication party (Alice) and the other communication party (Bob) share a secret key H and a communication text m Step i The communication party (Alice) first prepares one initial value v in the hexadecimal notation and an initial vector V, which is 128 integers having random numbers as component. Step ii The communication party uses the initial value v and the secret key H to encrypt the initial vector V. The result is computed in (mod p) to be a multiple-affine key system K. Further, a multiple-affine key system K[i].n is set using the secret key H as follows.
Step iii The communication party adopts the random number value x Step iv Finally, the communication party transmits {V, C} to the other communication party through a network. In such a way, since a third party other than the communication party and the other communication party does not know of a secret key H which is key information, the third party cannot obtain a multiple-affine key system K. Since many {initial vector V} exist, a different affine key K is used each time of encryption. Furthermore, random number sequences {r [High Speed Decryption] When the other communication party receives a communication text, the cipher text is decrypted in the following procedure: Step i The other communication party (Bob) encrypts K′ using the common key K with an initial value as x Further, H[i].n is also set using K as described above. Step ii When C is encrypted with H, then a communication text M can be achieved. In such a way, high-speed encryption can be realized, a processing speed can be increased by a factor of about 2.5 compared with the first embodiment in which security receives high attention. For example, when encryption is performed with the latest high-speed personal computer (made by Intel Co., loaded with CPU pentium II having an operating clock 450 MHz) on a file having 10485 Kbytes, it is confirmed that the encryption is completed in the order of 0.84 sec. This means that encryption is processed at a rate of 100 Mbits per second. This shows that the encryption is effected at a speed three times or more that in a case of all the existing encryption systems. The multiple-affine key system encryption system described in the embodiment defines an apparatus for generating a random number sequence with 8 bits. While the apparatus is realized by only software, random numbers can be generated at a rate of 100 Mbits per second. The random numbers are excellent in the following points: -
- The random numbers are generated at a higher speed than in the Lehmer method in which the processing is executed in prime number p (mod p);
- The random numbers are excellent in quality compared with those generated by the Lehmer method;
- The random number sequence generated by the above described algorithm has a very long cycle and thereby, the sequence can be regarded to have virtually no cycles;
- Even if the number of affine keys is increased in order to generate more complex random number sequence, a processing speed is not decreased, and
- Even if part of an affine key is altered into a key constituted of a higher degree polynomial so that the random numbers are improved, almost no speed reduction actually occurs.
For such features, even when a specific chip is produced in order to effect the above encryption processing, the chip can be applied to a chip for other types of a high-speed random number generation, one of which can utilize realtime application of the Monte Carlo method. The fourth embodiment, as shown in In A communication apparatus [First Communication Control Procedure] The first communication control procedure in a communication system having such a function is shown in Now, it is assumed as preconditions that common multiple-affine key systems K are respectively held by the affine key generation sections A multiple-affine key system is rewritten each time when communication is performed as shown That is, a multiple-affine key system is rewritten each time when new communication is performed and a rewritten multiple-affine key system is held in the affine key generation section However, since it is conceivable that both affine keys are not common with each other, for example when a trouble occurs on communication, it is desirable that a sequence that leads to recovery of a commonality in affine key on request from one party is provided. As such a sequence, it may be acceptable that affine keys on respective sides can be reset to affine keys set in predetermined initial setting conditions even by transmission of an affine key from one side. According to this method, since there is in principle no transmission of key information in communication between the transmitter side and the receiver side and in addition, key information is altered each time when new communication is performed, encryption with very high reliability, which is virtually impossible to decipher is realized. Furthermore, in this case as well, encryption can be processed at a very high speed by performing the encryption by the above described method. The fifth embodiment is, as shown in [Second Communication Control Procedure] The second communication control procedure in a communication system having such a function is shown in The method holds multiple-affine key systems K fixedly on both of a transmitter side and a receiver side as a precondition. Values obtained by encrypting random number sequences α, β and γ with the multiple-affine key systems K are used as multiple-affine key systems K On the transmitter side, since generated random numbers in the random number generation circuit The six embodiment specifies a communication system in which multiple-affine key systems K are exchanged between both sides in each communication by transmission of a secrete key H and random number sequences α and β between the transmitter side and the receiver side as shown in [Third Communication Control Procedure] The third communication control procedure in a communication system having such a function is shown in In the third communication control procedure, a procedure for sharing a multiple-affine key system is performed at first each time when new communication gets started using the Diffel-Helman key exchange. Specifically, when an operation is defined regarding a secret key H as a start of a multiple length integer or a finite extension field Z/p and random number sequences are α and β,at first the transmitter side generates a secret key H Then, the receiver side sends a secret key H Thereafter, transmission data ABC, DEF, GHI, . . . are transmitted after being encrypted with the multiple-affine key system K and the transmission data are decrypted with the multiple-affine key system K on the receiver side. In the third communication control procedure described above, while a time period of 1 to 2 sec is required for key exchange, encryption with low possibility in deciphering and high security is provided since key information is altered each time when a new communication is gets started. Incidentally, this method is suited to communication with low frequency. In the mean time, while the embodiment in which a multiple-affine key system is transmitted in each communication is described, there is no specific limitation to this case and, it is acceptable that, for example, control is effected so that multiple key exchange is conducted only in the first communication for the day or so that multiple-affine key system exchange is conducted at constant intervals. Besides, a further alternative method is not a key exchange in which affine keys are not exchanged randomly, but a key exchange in a recycling mode in which affine keys of predetermined kinds are sequentially substituted so as to go back to the start key at a prescribed cycle. That is, even if keys are changed in a recycling mode in which the same key is repeatedly used at constant cycle intervals, deciphering is practically impossible, so that high security can be retained. Besides, with the method, even if a discrepancy arises between states of affine keys on respective sides of a transmitter and a receiver, matching between affine keys on the respective sides can be easily achieved. For example, specific numbers are attached to respective keys in advance and then the specific numbers can mutually be notified to match the affine keys each other. The seventh embodiment is shown in Description will below be made of an authentication method for a specific other party in which such an encryption method and a communication control procedure for a cipher text are employed. There is substantially no deciphering method for a cipher text using the above described multiple-affine key system. Accordingly, an authentication method in which a third party cannot decipher the contents of authentication can be prepared by conducting authentication of a specific other party utilizing the cipher text. That is, a keyword or the like for authentication is given to an authentication object (authenticated party As a first authentication method, for example, a predetermined initial vector V is given to the authenticated party As a second authentication method, the authenticator party Description will be made of a concrete example below. As objects of authentication, the following cases are named. Incidentally, objects of application are not limited to those exemplified below, but cases of any authentication to specify an individual person or particular electronic devices are naturally included in the objects. The objects of application are: -
- (1) application of a multiple-affine key system for the above described encryption to authentication information on electronic transaction in which communication means such as internet is utilized;
- (2) application of a multiple-affine key system for the above described encryption to a keyword as a permit to receive pay television broadcasting;
- (3) application of a multiple-affine key system to authentication information to identify a particular electronic device, wherein electronic devices are respectively attached with a unique multiple-affine key system. For example, there can be named application of a multiple-affine key system for the above described encryption to authentication of communication permission for a radio device such as a portable phone in order to improve security of communication permission on the radio device; and
- (4) application of a multiple-affine key system to authentication information on an individual person, wherein individual persons are respectively attached with a unique multiple-affine key system.
Description will be detailed of communication control procedure for authentication with reference to The authentication object (authenticated party) It is assumed that common multiple-affine key systems are at hands of the authenticated party The authenticated party Thus generated multiple-affine key system K is used for encryption of the communication text. Then, a cipher text M′ prepared by encrypting the communication text M using the generated multiple-affine key system K is sent back to the authenticator party On the authenticator party In the mean time, in a case where identification of the authenticated party is difficult prior to the communication control procedure for authentication, it is acceptable as communication control procedure preceding the authentication to take a procedure in which information to identify the authenticated party, for example, ID number information of the authenticated party is inquired to obtain the ID number information and then, a multiple-affine key system of the authenticated party is retrieved on the basis of the ID number information. Even in such a control, since there is adopted an encryption method for authentication in which only an ID number information is transmitted and there is no chance for a multiple-affine key system to be transmitted and therefore, a multiple-affine key system is not deciphered, authentication with very high security can be achieved. Further, as another authentication method, the authenticator party Then, the authenticator party When a cipher text obtained by any of the encryption methods described above is decrypted in a procedure similar to the above procedure, and then authentication is performed on the basis of whether or not decryption is correctly effected, authentication with high security can be achieved. The eighth embodiment is shown in In The communication apparatuses Besides, in the router device In such a configuration, the router device The ninth embodiment specifies, as shown in FIGS. An encryption/decryption method using a multiple-affine key system of the present invention efficiently is realized, for example, as an application computer program on a personal computer. The reason why is that the computer is provided with necessary functions including various kinds of setting for encryption/decryption, reading and storing encrypted and decrypted files and the program can be easily operated like compression/decompression of a file. Below, fundamental operations will sequentially be described mainly on the basis of the flowchart with reference to operating screens. The program that has been initialized (S Now, description will be given of operations of the program according to a procedure of encryption/decryption of one document file based on the program. First, the number Then, since a screen Likewise, in the decryption, a file to be decrypted is designated on a screen Further, the program can generate a new multiple-affine key system (S As described above, according to the program, encryption/decryption using a multiple-affine key system with very high confidentiality and a high speed in processing can be realized by easy operations, for example, on the computer system of Incidentally, the application program may be stored in, for example, a medium that is readable by a computer system and besides, the application program may be stored in advance in a storage area of ROM and the like in the computer system The tenth embodiment specifies, as shown in A recording/reproduction device for the record medium is, for example, a device used for a demountable or non-demountable record medium such as a floppy disk, hard disk or MO, and the fundamental configuration is shown in With such a configuration, in the medium recording/reproduction device, the record medium Further, in reading, the above described encrypted information is read from the record medium In embodiments of encryption/decryption in read/write operations, not only the first to third embodiments but various modifications of the embodiments can naturally be allowed. That is, a multiple-affine key system may be one stored in advance or a multiple-affine key system may be one specified by a secret key H given from the interface section Further, the encryption/decryption may automatically be performed in read/write operations all time and may selectively be conducted on the basis of setting by a user. According to the present invention, in any case of application, there can be provided a medium recording/reproduction device with very high confidentiality, which is very difficult to be deciphered, by using a multiple-affine key system automatically rewritten. The eleventh embodiment is shown in The embodiment is to apply an encryption/decryption method of the present invention to an optical disk recording/reproduction device in which data (information) is recorded on an optical disk (for example, DVD-RAM) In In such a configuration, recording of information on the optical disk Of course, encryption in the multiple affine encryption section Further, reproduction of information recorded in the optical disk Details of the encryption/decryption in this case can be explained with the respective embodiments described above. That is, as an example, a multiple-affine key system used for generating random numbers may be stored in the memory As described above, in an optical disk recording/reproduction device as well, when encryption/decryption using a multiple-affine key system having a self-rewrite function of the present invention is applied, an optical disk recording/reproduction device with high confidentiality, which is hard to be read by a third party, can be provided. The twelfth embodiment is shown in A fundamental configuration of the radio transmission/reception device is shown in Description will be made of reception in the transmitter/receiver with such a configuration. A forward link signal transmitted from a base station is received by the antenna The modulation/demodulation section Therefore, there can be realized decryption of encrypted information with very high confidentiality using a multiple-affine key system rewritten each time when the number of use times of a multiple-affine key system reaches a predetermined number thereof. Besides, the decryption in this case can be performed in a form according to any of the above detailed embodiments. As an example, the case of the second embodiment is named, wherein a secret key H and an initial vector V are received together with a cipher text, affine keys corresponding to those are generated when a need arises, random number sequences are also generated using the affine keys and eventually decryption is performed by the random number sequences. Thereby, decryption with a-new affine key can be effected for each communication. Description will be made of transmission of the radio transmitter/receiver below. A reverse link signal transmitted from a mobile station is given to the vocoder In such a manner, a radio signal encrypted using a multiple-affine key system rewritten in each time when the number of use times of the multiple-affine key system reaches a predetermined number has high confidentiality since deciphering by a third party is impossible. Further, needless to say that an embodiment of encryption can be those in the above detailed embodiments. For example, a multiple-affine key system may be stored in a memory or the like in advance, alternatively may be a new one generated on the basis of a secret key H and an initial vector V from the demodulation section In a radio transmission/reception device such as a portable phone as well, as detailed above, an encryption section and a decryption section using a multiple-affine key system of the present invention are adopted, thereby speech communication with high speed and very high confidentiality can be realized. According to the present invention, as described above, there is provided an encryption method and an encryption system with variety of applications, which not only enables high-speed encryption but makes deciphering by a third party impossible. Further, since stream encryption is employed using random numbers and a multiple-affine key system, a high security, high-speed encryption method is established while refusing a known plain text attack. In cipher text communication, since a multiple-affine key system for encryption are shared between communication parties, a cipher text can be transmitted without transmission of key information for encryption and encryption communication with high security, which is very hard to be deciphered, can be realized. Further, as in the fifth embodiment ( Further, as in the sixth embodiment ( Further, as in the seventh embodiment ( Further, as in the ninth embodiment (FIGS. Further, as in the tenth and eleventh embodiments ( Further, as in the twelfth embodiment ( Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents. Referenced by
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